This project is concerned with the synthesis and biologic evaluation of selenium containing analogs of a) aromatic amino acids as imaging agents for the detection and differential diagnosis of carcinoma of the pancreas, b) inhibitors of adrenocorticosteroid biosynthesis for the analysis of adrenal cortex pathology, c) levamisole, and immunopotentiating agent, for the analysis of the immune response in cancer patients, d) estradiol for the detection and diagnosis of breast cancer, and e) CNS active drugs for the detection of brain neuropathy. The research goals for this year include evaluating selenium containing analogs of phenylalanine and tryptophan, metyrapone, estradiol and guanosine. These compounds will be administered to rats to determine their pharmacokinetics, biologic distribution, toxicity and ultimate fate. Selenium levels in the tissues will be determined by neutron activation analyses. Those agents that demonstrate in vivo stability and promising target-to-nontarget-organ ratios will be labeled with 75Se and reevaluated using the gamma well counter to determine tissue distribution.